When you get to the sales tax deduction section, you can report your child support received. The sales tax deduction is based on your income because it makes sense that if you have more income, you'll have more stuff, and therefore pay more sales tax. So, make sure you report it there to increase your income for that section. It stil won't be taxed, though, so no worries there.

On your federal taxes, if you itemize decudtions, you can either deduct your state income tax or sales taxes. (This benefits people who live in a state with no income tax). What the PP is saying is that in determining the amount of "sales tax" that can be deducted, you can increase it by adding your child support received to your income.